Afterburner fuel system with pump unloader



Dec. 23, 1958 G. E. HOLBROOK 2,865,166

AFTERBURNER FUEL SYSTEM WITH PUMP UNLOADER Filed June 11, 1952 14/1. 7- Flam Inventor Attorneys United States Patent "ce AFTERBURNER FUEL SYSTEM wrrn PUMP UNLOADER Gordon E. Holbrook, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Micht, a corporation of Delaware Application June 11, 1952, Serial No. 292,940

2 Claims. (Cl. 6035.6)

This invention relates to turbo-jet engines and more particularly to an afterburner fuel system for a gas turbine engine.

An object of this invention is to provide a means whereby the fuel flow to the afterburner may be quickly initiated or stopped without adversely affecting the afterburner fuel pump.

Other objects of this invention are to provide a means whereby an afterburner fuel pump may be prevented from overheating and overloading.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of the present invention is clearly shown.

In the drawings: of a turbo-jet engine including an afterburner and the fuel system associated therewtih and Figure 2 is a schematic illustration of a partial modification of Figure 1.

Referring now to the drawings in detail, it may be pointed out that the details of the turbo-jet engine as such are immaterial to the invention and that the invention may be incorporated in turbo-jet engines of various configurations. The invention is directed to an afterburner fuel system, and therefore the known type of turbo-jet engine that is shown will be described only briefly. The engine comprises an outer casing within which is an axial flow compressor rotor 11 that is connected by a shaft 12 to an axial flow turbine 14. An inner casing 15 cooperates with the outer casing 10 to define an annular combustion chamber or combustor that includes the perforated flame tubes 16. The outer casing 10 terminates in a jet propulsion nozzle 18 which may have its discharge area varied by the movable eyelids -19 that pivot at 20. A tailcone 21 supported by the radial struts 22 and the afterburner fuel nozzles 24 that are fed from the ring manifold 25, lie on the exhaust side of the turbine in the aft portion of the casing 10. The main fuel nozzles 26 that feed the flame tubes 16 are fed by the ring manifold 28.

In operation, air is drawn into the casing 10 and compressed by the compressor 11. The compressed air flows into the. flame tubes 16 where it is mixed with the fuel that is injected by the nozzles 26 for combustion.

The compressor supplies a larger amount of air to the combustion chamber than is actually required for combustion because of the temperature limitations that are imposed by the materials that are presently utilized in turbine constructions. According to present day practice only some 25% of the oxygen is actually burned,

Figure 1 is a schematic illustration Patented Dec. 23, 1958 so the gases that exhaust from the combustion chamber' comprise a mixture of the actual products of combustion' and the unburned air that flows through the nozzle ring 29 to impinge upon the blading of the turbine 14 to drive the same. The gases that exhaust from the turbine are discharged from the jet propulsion nozzle 18 to furnish the motive power for the aircraft or other conveyance in which the turbo-jet engine is installed.

When it is desired to augment the velocity of the turbine exhaust gases to increase the jet propulsion effect of the engine the afterburner is put into operation. Afterburner operation includes the opening of the eyelids 19 which may be effected by any suitable mechanism so as to attain a maximum nozzle discharge area and the injection of fuel into the aft portion of the casing 10 by the afterburner fuel nozzles 24 for combustion with the unburned air of the turbine exhaust. Afterburners are generally operated only when an aircraft is at extremely high speeds and altitudes or when it is desired to impart maximum power to an aircraft, for they are too ineflicient to be used during normal flight conditions. Because of this and because ofdiversities that exist between the characteristics of the main and afterburner combustion chambers it is necessary to provide the afterburner with an independent fuel control.

In the fuel system that illustrates my invention, a suitable fuel such as kerosene is taken from a reservoir (not shown) and forced by a booster pump 30, which may be electrically driven, through a line 31 to the main fuel pump 32 and to the afterburner fuel pump 34 through lines 31 and 33. The pumps 32 and 34 are preferably gear type pumps and are driven by the shafts 35 and 36 which are suitably geared to the drive shaft 12 for rotation thereby. Fuel from the main fuel pump 32 is metered by the main fuel control 38 and is fed by the line 39 to the manifold 28 for discharge by the main fuel nozzles 26. A line 40 serves to by-pass excess fuel from the main fuel control back to the intake side of the main fuel pump 32. The details of the main fuel control are not shown, being immaterial to my invention.

The afterburner fuel pump 34 discharges into a line 37 to supply fuel to the afterburner fuel control 42 which feeds a metered supply of fuel to the afterburner fuel nozzles 24 through the line 44 when afterburner operation is effected by the switch 45. A relief valve 46 connects the line 37 to the line 48 that leads to the inlet side of the pump 34- to by-pass excess fuel around the pump. The valve 46 is normally closed, and is set to open only at a high pressure such as would be built up should there be a failure in the by-passing feature of the afterburner fuel control 42.

The afterburner fuel control 42 includes a metering valve 49 operated by the bellows 50 through the pivoted link 51. The bellows 50 is provided with a spring 52 and an adjusting screw 54. The bellows 50 is provided with means for sensing the afterburner fuel demand by subjecting its exterior to the compressor discharge pressure and its interior to the compressor inlet pressure, as the compressor pressure rise is an indication of mass air flow. The lines 55 and 56 are connected in any suitable manner to the compressor to supply these pressures-to the bellows 50. The area of the metering valve opening is determined by the difference between these pressures acting against the spring 52. The fuel flow varies directly with the area and thus will vary directly with the differential in pressures. The metering valve 49 is therefore responsive to the differential in compressor inlet and outlet pressures and being a balanced type valve will be unaffected by fuel pressure variations, with its movement solely dependent upon the movement of the bellows 50. A pressure regulator valve 58 is provided to maintain a constant fuel pressure drop across the metering valve 49 and to act as a by-pass to return excess fuel to the afterburner fuel pump inlet through the line 48. A spring 59' and adjusting screw 60 are provided to set the amount of fuel pressure drop across the metering valve 49. Since the inlet and outlet pressures at the metering valve 49 will act in opposition on the ends of the regulator valve 58, the desired. pressure drop across valve 49 is maintained by the spring 59, valve 58 moving to throttle the by-pass to achieve this result.

In operation, an increase in compressor discharge pressure will indicate an addition in the mass air flowto the afterburner and the bellows 50 will contract to increase the degree of opening of the metering valve 49 thus supplying more fuel to the afterburner fuellnozzles 24. Conversely, a decrease in compressor discharge pressure will result in less fuel being supplied to the arterburner fuel nozzles 24.

My invention is particularly directed to the means for preventing the afterburner fuel pump from overheating. As previously noted, the afterburner is subect to intermittent operation while the main combusa t1on system operates continuously; and the afterburner fuel pump 34, being engine driven, will also run continuously. When operation of the afterburner is desired, the switch arm 45 is engaged with the contact 61. to energize the coil 62 of the afterburner fuel shut-off valve 64 to open the same against the action of the spring 65. The afterburner is shut off by engaging the switch arm 45 w1th the contact 66 thus breaking the circuit to the coil 62 to permit spring 65 to cut off the fuel supply to the afterburner fuel nozzles 24. Engagement of the:

switch 45 with the contact 66 will energize the coil; 68 of the valve 69 to open the same against the action. of the spring 70. The opening of the valve 69 will dump fuel from the underside of the piston 71 of the regulator valve 58 through the line 48 to the inlet side of. the afterburner fuel pump 34. This will reduce the pressure under the regulator valve 58 and permit it to open so that the regulator valve can also by-pass fuel back through the line 48 to the inlet side of the afterburner fuel pump 34. The afterburner fuel pump 34 will thus be working only against the action of the spring 59 and the pump 34 will be practically unloaded as this spring is relatively weak. The relief valve 46. is provided. to by-pass fuel around the pump only under a high pres-- sure such as would be developed if the valve 69 failed to open. Although the pump 34 is practically unloaded while the afterburner is inoperative there is still some heating of the pump and a small orifice 72 is provided to bleed away some of the fuel to cool the pump. The fuel may be conveniently led through a line 73 to the inlet side of the main fuel pump 32 or back to the fuel reservoir or recirculated through a heat exchanger. The orifice 72 bleeds away such a small amount of fuel as will have no significant effect upon the capacity of pump 34 when the afterburner is in operation.

Figure 2 illustrates amodification of the-fuel system shown in Figure 1 that eliminates the necessity for. the' bleed. line 73. In the modification the bleed line 73 is omitted and the afterburner fuel pump relief line 48 is connected to the main fuel supply line 31 rather than. to the afterburner fuel pump supply line 33. The

desirability of this modification is somewhatdependent.

It should. be apparent that the afterburner fuel control may be used to advantage with any type of fuel pump that is continuously driven and that the invention eliminates the need of a clutch or similar device to protect the afterburner fuel pump, or the provision of an indirectly driven pump with means for deenergizing the pump driving motor. The need for the invention can be readily realized when it is understood that a typical afterburner may consume fuel in excess of 20,000 pounds per hour, so that pump 34 is of relatively large capacity.

The preferred embodiment of the invention has been described fully in order to explain the principles of the invention. It is to be understood that modifications of structure may be made by the exercise of skill in the art within the scope of the invention which is not to be regarded as limited by the detailed description of the preferred embodiment;

I claim:

1. A gas turbine comprising a compressor for supplying air to a combustor, said combustor supplying motive fluid to a turbine to drive said compressor, a jet exhaust duct for said turbine, an' afterburner in said exhaust duct, means for supplying metered fuel to said combustor including a combustor fuel pump and a combustor fuel control device, means for supplying metered fuel to said. afterburner including an. afterburner fuel pump andanafterburner fuel control device, and means for continuously driving both of said pumps during the operation of. said. turbine and compressor, said afterburner. fuel control device including a fuel supply passage connecting the outlet side of said afterburner fuel pump and the inlet side of said afterburner, a fuel return passage connecting said. fuel supply passage to the inlet side-of said. afterburner fuel: pump, a pressure regulator valve in said fuel return passage for controlling the return. of fuel from said fuel supply passage to the inlet side of said afterburner fuel pump, a metering valve in said fuel supply passage downstream of said pressure regulator valve for regulating the flow of fuel to said afterburner, a shutoff valve insaid fuel supply passage downstream. of saidmetering valve for stopping the fiow of. fuel. to said afterburner, said pressure regulator valve: including a pistonportion having a first side communicating with said. fuelreturn passage and a second side communicatingwith said' fuel supply passage downstream of said metering valve and upstream of said shutoff valve and. including a lightspring arranged to bias said pressure regulator. valve in. closing direction, a relief passageconnecting said fuel return passage with. said second side of. said piston portion, and-a controlvalve in. said relief. passage arranged to open on closure ofsaid shutoff valve to provide. a drop in. fuel pressure on said second side of saidpiston portion whereby said pressure regulator. valve will function as a negligible resistance relief. valve. for said afterburner fuelpump to unload the same when the flow of fuel to said afterburner isstopped by the closure of said shutoff valve.

2. A. fuel control system comprising a fuel burning device,.a fuel pump arranged to run at times when the fuel burning device is inoperative, and a fuel control device comprising a supply passage connectingthe outlet side of the pump and the inlet side of the burning device, a

return passage connecting the supply passage to the inlet side of the pump, a pressure regulator valve in the return passage for controlling the return of fuel from the supply passage to the inlet side of the pump, a. metering valve" in the-supply passage downstream of thepressure regulator valve for. regulating the flow of fuel to the burning device, a shutoff valve" in the supply passage downstream of the metering valve for stopping the flow of fuel to the burning device, the pressure regulator valve including. a piston portion having a first side communreating. with. the return passage and a second side communicating with the supply passage downstream of the metering valve and upstream of the shutoff valve and including a light spring arranged to bias the pressure regulator valve in closing direction, a relief passage connecting the return passage with the second side of the piston portion, and a control valve in the relief passage arranged to open on closure of the shutofi valve to provide a drop in pressure on the second side of the piston portion whereby the pressure regulator valve will function as a negligible resistance relief valve for the fuel pump to unload the same when the flow of fuel to the burning device is stopped by the closure of the shutofl valve.

References Cited in the file of this patent UNITED STATES PATENTS Holley Aug. 13, 1946 Bobier Feb. 28, 1950 Schmitt Sept. 5, 1950 Orr Mar. 20, 1951 Orr Aug. 14, 1951 Redding Sept. 4. 1951 Lombard Apr. 13. 1954 FOREIGN PATENTS France July 19, 1948 

